Spark-gap apparatus



F. LOWENSTEIN.

SPARK GAP APPARATUS.

APPLICATION FILED 1AN. 19, |918.

1.888.888. www@ Aug. 23, 192A.

7 SHEETS-SHEET l4 C1 ttozne g F. I OWENSIEIN.

SPARK GAP APPARATUS.

APPLICATION FILED JAN. I9, 1918. lgh Patented Aug. 239 H2L NYSHEETs-SHEET 2.

I ji/@wem F. LOWENSTEIN.

SPARK GAP APPARATUS.

APPLICATION F1150 11111.19, 1918,

19388,@314511 Patented Aug. 239 1921.,

YSHEETS-SHEET 3.

F. LOWENSTEIN.

SPARK GAP APPARATUS.

A PPucMrLoN F1LED`1AN.19. 191s.

1921. SHEET 4,

.Patented Aug. 23

7 SHEETS- a num/W01 (1R01 ne nl;

F. LWENSTEN.

SPARK GAP APPARATUS.

APPLICATION HLED sAN. 19. m.

SHEET 5,

F. LOVVENSTEIN.

SPARK GAP APPARATUS.

APPLICATION, FILED IAN. I9, i913.

Patenel Aug 239 H2L YSHEE fS-SHEET 6.

F. LOVVENSTEIN.

SPARK GAP APPARATUS.

APPLICATION FILED IAII. I9, 191s.

Patent@ Aug. 239 1923,

icao

SPARK-GAP JPPARATU S.

Specication of Letters Patent.

Patented Aug'. 23, 11921.

Application tiled January 19, 1918. Serial No. 212.616.

To all lwhom t may concern:

Be it known that I, FRrrz LOWENSTEIN, a citizen of the United States,residing at Brooklyn, county of Kings, and State of New York, haveinvented certain new and useful Improvements in Spark-Gap Apparatus; andl do hereby declare the following to be a full, clear, and exactdescription of the invention, such as will enable others skilled in theart to which it appertains to make and use the same.

This invention relates to radio signaling apparatus. 1n particular, ithas to do with a novel type of quenched spark gap apparatus for use inradio transmitter systems.

ln what is generally known in the radio art as the quenched gap, thetotal operating gap length or distance is split up into a plurality ofrelatively minute gap distances which are in series electrically andwhose sum gives the necessary length and power of disruptive sparkdischarge necessary for operation under given conditions. rllheadvantages of a quenched gap, as against the older type of single fulllength gap, are well known in the art and require no recital here. Theuse of the quenched gap has been attended, however, with certaindiiiiculties and drawbacks in practical radio work which it is the mainobject of this invention to overcome, while also attaining betteroperation and greatly increased convenience and general efficiency. 1nthis connection reference is here made to my prior application,copending herewith, Ser. No. 858,499, iled August 25, 1914, which hasmatured into Patent No. 1,305,816, of June 3, 1919, in which certainbroad features characterizing the invention hereinafter set forth andclaimed, are dis closed. Said prior application relates particularly toquenched tubular gaps. The present disclosure has to do more especiallywith quenched gaps of the plate or disk type, though in its broaderaspects the invention is not limited thereto.

Among the disadvantages 'inherent in quenched spark gap apparatusproposed prior to'my invention was the diculty of removing and replacingindividual gap units from the assembled series when necessary. Theentire gap had to be taken apart and reassembled, an loperation whichrequired considerable technical skill and which involved serious delayand inconvenience. One of the objects'of my invention is to provide aquenched spark gap of such improved construction that any one of thecomponent gap units, which may comprise a single elemental gap orseveral elemental gaps, can be readily removed and replacedindependently of the rest and without in any way disturbing theirrelation to one another. In particular, the object of the invention inthis respect is to provide a plate gap construction of the aforesaiddesirable characteristics, that is, a quenched gap inwhich the componentgap units consist of pairs of spaced plates or dlsks, constitutingelectrodes between which then elemental spark discharges occur seria y.

rlhe problem of properly cooling quenched gaps, especially gaps of anyconsiderable power, has also been a serious one. Cooling by means of afan has been commonly re sorted to, but this requires auxiliaryapparatus and introduces attendant complications which it is oftendesirable or essential to avoid. Self-cooled gaps have been knownheretofore, but they have been characterized by massive heat-radiatingsurfaces of large size and weight, rendering the gap very bulky, heavy,and unsuited for use except where economy of space and ready portabilityof apparatus are of no particular consequence.v An important object ofthe present invention is to provide a self-cooled gap whose size andweight for a given power rating are Very much less than has beenpossible heretofore.

Another object of the invention is to enable the efective number of gapunits or elements in circuit to be varied easily and rapidly inaccordance with requirements of practical operation, so that, forexample, the

power of the gap may be varied in relatively.

large steps, or 1n small steps, or according to both methods.

With the foregoing general objects in view, as well as others which willbe apparent to those skilled in the art from the following description,my invention consists in the novel construction and arrangement ofparts, considered both broadly and specifically, hereinafter set forthand as pointed out in the appended claims.

For the sake of clearly illustrating andexplaining the nature of theinvention and its underlying principles so that the invention may bepractised by those skilled in the art, I have shown in the accompanyingdrawings vcertain structural embodiments of the invention which atpresent ll consider 'widely therefrom in mechanical details andarrangement, while still embodying the broad'principles of theinventionand krealiz,- ing its benefits to a greater or less extent.

In the accompany-ing drawings, illustrat ing certain especiallydesirablel forms of apparatus wlthm the lnventlon,

Figure 1 1s an end elevation vof a Spark gap apparatus, comprising aholder with spark gap units mounted thereon, the spark gap being lhereshown associated with other parts of a wireless transmitter;

Figs. 2 and 3 are a front elevation and a partial top plan,respectively, of said spark gap apparatus;

Figs. 4 and 5 are a longitudinal section and partial end view,respectively, of one form of spark gap unit or element employed;

Fig. 5a is a fragmentary section on the line {ia-45a of Fig. 5;

' Fig. 6 is a section of a slightly different gap unit construction; j

Figs. 7 and 8 are a partial front elevation and a sectional end view,respectively, showing another type of holder for the gap units;

Figs. 9 and 1() are a top and side view, respectively, of a detail ofthe construction shown in Figs. 7 and 8;

Fig. 11 is a sectional view showing still another construction of sparkgap unit;

Fig. 12 is an end view similar to Fig. 1, of another modified type ofholder for the spark gap units, partly broken away for the sake ofclearness; and

Fig. 13 is a front elevation partly in section, of the apparatus shownin Fig. 12, with the front part of the holder removed and some of thespark gap units omitted for the sake of clearness in illustration.

Referring first more particularly to the ga vunits themselves, adesirable form of unit is illustrated by way of example in Figs. 4 and5, where 20 and 21 are circular spark gap plates or disks of brass orother I suitable conducting material, having recesses i here shown ascomprising a bolt 23, desirably of bronze, whose head is arranged toexert tends -loosely through clamping pressure on plate 21, thoughinsulatedtherefrom. To this end said bolt exressure washer 24, andthrough an ample c earance opening 25, in plate 21, and is threaded at26 to engage the threaded lbore 27 in plate 20. As here shown, the boreextends completely through the plate but is closed at its outer end bycover plate 28, soldered to plate 2O. This is merely a manufacturingexpedient, it being simpler to do this than to bore a hole part waythrough the plate to an exact desired depth.' An insulating washer 29separates pressure washer 24 from plate 21; while insulating gasket 30separates the relatively narrow cooperating bearing flanges or ribsprovided on the ad'acent faces of the spark gap plates near t eirperipheries. These bearing flanges or ribs are slightly rounded asindicated at 300 in order to insure efiicient and accurate seating ofthe coperating disk members against the. insulating gasket 30,

ressure on the gasket 30" being thus as to p-rovide a sealed joint, itis desirable v that the under surface 230'of said bolt head be beveledat a slightly greater angle than the coperating bearing surface 241 ofsaid washer. In practice, the angle of the surface 230 may be 45, forexample, while that of the surface 241 may be about 40. This gives alinear bearing contact between the bolt and the washer so that when thebolt is turned down to seat against the washer it grinds into the metaland gives a close sealed joint. As will appear hereinafter, it is notessential to employ the pressure or bearing washer 24; but it is verydesirable to do so since in this Away it is ossible to avoid abradingaction of the bo t head on the insulating washer 29 incidental to directcontact of the bolt head therewith. It is evident that by means of thegap unit construction described, the two spark gap plates or disksforming the elementary gap electrodes,

are electrically insulated from each other, and the sparking surfacesare inclosed in an alr-tight chamber. The described arrangement forclamping together the component members of the gap unit while capable ofwide variation in detail within the scope of the invention, insuresaccurate and uniform spacing apart of the sparking surfaces. When anumber of gap units are assembled in series, flange 210 of one unitcooperates with flange 200 of the next succeeding unit to space the headof bolt 23 away from plate 2O of such succeeding unit and thus toprevent short-circuiting an elementary gap.

messer. g

Provision is made for dissipating the heat generated by the spark gapunits, and in the construction illustrated the gap is designed to beself-cooling, that is, to be operable without a fan or other auxiliarycoolin means. rlhis construction departs radically from the priorpractice in this art. Heretofore cooling fins or flanges have been caston spark gap disks or plates, and have been of the same material as thedisk or plate, ordinarily brass. Furthermoresuch flanges have been ofrelatively very thick cross section. ln such prior practice,thetemperature gradient has been low, the difference in temperature betweenthe base of the fin or flange next to the electrode, and the outerextremity of such fin ordinarily not amounting to more than about 1 C.This former type of construction resulted in massive heavy spark gapapparatus, as hereinbefore pointed out, ln contrast to the priorpractice, l have found that the use of thick heavy metal flanges or nsfor the gap electrodes is entirely unnecessary, and that a very muchmore efficient cooling effect is obtained by employing fins or fiangesof relatively very thin cross section, most desirably of sheet metal,formed separately from the electrodes and attached thereto in heatconducting relation; and that by means of this improved construction,the weight of spark gap apparatus can be reduced, for example, toonethird of the minimum weight at which it was possible to constructself cooled spark gaps heretofore. ln spark gaps constructed inaccordance with this particular phase of the present invention, it hasbeen found desirable in actual practice to have a relatively hightemperature gradient such, for example as to give under usual operatingconditions a difference in temperature between the central and outerportions of the cooling flange or iin amounting to as much as l()o C.;and for the purposes of this invention, such temperature gradient shouldordinarily be high enough to give a tem erature difference of not lessthan 3 or 4 that is to say, sveral times as greata temperature gradientas has been heretofore employed in this art. ln addition to the broadnovelty involved in the use of relatively very thin heat dissipatingflanges for the electrodes, :and especially sheet metal ns, the presentconstruction is further characterized, in the most desirable embodimentof the invention, by an arrangement of Vsaid flanges or fins in suchmanner as to provide air circulation passages or channels in the natureof ,fines or chimneys, whereby systematic and efiicient circulation ofcooling air over broad heat dissipating surfaces is accomplished.Evidently the broad principles involved in spa-rk gap cooling means ofthe character described can be embodied in various forms mechanically,but the construction here illustrated by way of example have 'vensatisfaction 1n practice and is particu arly desirable.

Referring again to Fig. 4, the cooling g means here shown comprisesdouble rectangular flanges or fins 3l, one or more such double flangesbeing provided for each gap plate. It is especially desirable to formeach of these double flanges or fins of two sheets of highly conductivemetal, such as cold rolled copper. the sheets being centrally aperturedand oppositely flanged as indilcated at 32, Where they fit snugly aroundand are soldered to the gap plate. The sheets Aare folded or lapped overeach other and most desirably soldered together at the corners or atpoints along one pair of opposite outer edges,'as indicated at 33, theother pair of edges 34C' being left substantially free. ln use, theedges 33 are vertical, the double fin arrangement thus acting like a.chimney fiue and favoring Veihcient air circulation upwardly over theheat dissipating surfaces provided by the copper sheets of the doubleflange. rlhe rectangular boxlike construction of the double flanges,open at top and bottom and closed on the sides, acts like a flue or achimney, the heat given o by the copper flanges when the gap is in useserving to establish a natural draft vertically over the flangesurfaces, and thus rendering unnecessary the employment of auxiliarycooling means. rlhe same action occurs to a somewhat less extent in thespaces between the double flanges of each pair of electrodesconstituting a unit, and also betweenthe flanges of successive unitswhen they are assembled in series.

As a further aid in stiffening the double cooling flange construction,one or more tongues 310 may be punched from one or both of the componentmetal sheets 3l, as shown in Figs. 5 and 5a, to form a brace betweensaid sheets. For convenience in assembling the parts of a gap unit,three of the four sheets comprised in the two double flanges areprovided with three sets of alined holes 311, the radial distance ofthese holes from the axis of the gap unit being substantially equal tothe outer radius of the insulating gasket 30. With the aid of assemblingrods extending through the several sets of alined holes, the insulatinggasket can thus be accurately centered with respect to the coperatingpressure fianges which is somewhat greater than in the unit of Fig. -'l.This is rendered necessary by the fact that the plate 21 of the gap unitis thinner than the corresponding plate 21 shown in the correspondinggap unit of Fig. l. Consequently it is desirable that the clampingpressure exerted by the bolt 23 on the bearing washer 24 be applied tothe plate 21 at points considerably nearer the peripheral bearingflanges 300a of the electrodes, in order to avoid affecting theelementary gap distance when the bolt is tightened up to clamp theelectrodes together. Because of the greater diameter of the washer 24,and the consequently smaller 1nsulating air space between the edges ofthe washer, and the flange 210, the insulatlng washer 29a is made cupshaped as shown to avoid any possibility of short circuiting theelementary gap.

The type of spark gap unit illustrated 1n Fig. 11 involves the samegeneral princlples of construction as those hereinbefore described. Theprincipal detailed differences are the employment of triple coolingflanges 31b in place of double flanges, and the employment of a clampingbolt 23b whose head 23 bears directly on insulating washer 29b insteadof through a protecting pressure washer. As here shown the flanges 31bengage shoulder 31c formed on the peripheries of the electrode plates,this arrangement favoring stiffness and rigidity of the assemblage. Thebolt head may be slotted at 23d to receive a wrench, and the electrode20b may also be provided with wrench receiving recesses as indicated at20, this arrangement being convenient in assembling the gap electrodes.The electrodes 20 and 21b may be advantageously cutaway somewhat at theouter edges of the sparking rings as indicated at 201 to confinesparking strictly to the sparking rings.

The three typical constructions above described for the spark gap unitsmay be employed in spark gap apparatus of different operating powers,and may of course be varied in dimensions. as required for service underdifferent conditions. However, since self cooled spark gap devices ofthe construction herein disclosed are broadly novel, and for the sake ofaffording concrete examples ofself cooled spark gap units which willgive satisfactory results in actual use, examples of certain dimensionsand proportions which have been demonstrated to be suitable will begiven by way of explanation. Assume that fifteen gap units are to beemployed in series for operation at full rated power. On thisassumption, spark gap units for two kilowatt operation, constructed inaccordance with the showing of Figs. 4, 5 and 5a may have the followingprincipal dimensions: The silver spark rings 22 have an inside diameterof .625 inch and an outside diameter of 1.25 inches; the brass electrodeplates or disks are 2 inches in diameter and have a thickness of from .3to .4 inch at the locality of the spark rings; the rectangular doublecooling flanges are 6 inches in vertical height and 5.25 inches inwidth; and the cold rolled copper of which the flailges are composed hasa thickness of .022 inc Under the same assumptions, a spark gap unit ofthe type illustrated in Fig. 6 and designed for operation at 1 kilowatt,may have approximately the same dimensions as specified above, but theelectrode member 21a may be thinner because less heat will have to bedissipated, and for the same reason the cooling flanges may have avertical height in this case of only 3.75 inches, and a width of 5.25inches. The electrode member 20a is of the same thickness as before inorder that it may not be sprung inwardly by the tension of theassembling bolt and the elementary gap distance thereby affected.

.For 5 kilowatt operation, a unit of the construction shown in Fig. 11may have sparking rings whose outside diameter is 1.75 inches and insidediameter .625 inch; electrodes 2.50 inches in diameter and .4 to .5 inchthick at the region of the sparking rings; the outside dimensions of thetriple cooling flanges being 7 inches vertical height and 8 incheswidth. The same thickness of sheet copper may be employed as before,namely, .022 inch. This approximate thickness g1ves particularly goodresults. In general, it is not desirable to use metal thicker than about.05 inch for the cooling flanges of gap devices of the type hereindisclosed.

The distance between adjacent cooling surfaces in these multiple fla-ngeconstructions is a point of considerable importance. I have found that,in general, with gap devices of the character herein described, bestresults are obtained when the spacing distance between adjacent fins isfrom .2O inch to .40 inch. Above or below these approximate limits, thecooling effect decreases rapidly. A range of from .25 inch .to .35.inchis especially desirable; and in the specific dimensioned examples abovegiven, a s acing distance of .28 inch between the slieet copper fins ofthe double and triple cooling flanges was found most suitable underpractical conditions. It is desirable also that the spacing betweenadjacent complete flanges as well as between the component flangeelements be within the limits just specified, uniformity of spacingfavoring uniformity in the gap performance.

It is to be understood that the foregoing dimensions are in no senselimiting and are here given merely as illustrating typical practicalconstructions which have proved especially satisfactory in actual use,particularly with respect to self cooling capability.

aeeaeee The dimensions given may of course be varied'considerablywithout departing from the invention and without sacrificing itssubstantial benefits.

lt is also to be noted that while the gap units here illustrated eachcomprises a pair of electrodes coperating to form a single elementarygap, the invention is not limited to such construction but contemplatesbroadly the combination in a unitary structure of a plurality ofelectrodes coperating to provide an elementary gap structure, several ofsuch elementary gap structures or units being adapted for arrangement inseries to constitute a complete quenched gap, of which the severalunitary parts are individually removable from the series withoutdisturbing the other members thereof.

Spark gap units of the character hereinbefore described may be assembledin series in any suitable type of holder or support.

Figs. l, 2 and 3 illustrate a method of mounting and electricallyconnecting in series a plurality of spark gap units or elements which lhave found especially de sirable in practice. As here shown, the gapunits, which in this instance are oi the type shown in Figs. 4 and 5,are supported on a substantial frame-work or holder of insulatingmaterial, consisting of upright end members 35, and horizontallongitudinal bars 36, 36a.. in the present example, the spark gap holderis intended to be associated mechanically with other parts of atransmitter construction, and to this end the end members 35 areextended, as shown in Fig. l, to support a condenser 37, and a panel 38for certain or the transmitter helices (not shown). As the presentinvention is not concerned with the details of these other parts, nofurther description of them is necessary. flhe spark gap units, of whichthere are lifteen in the present example, may be mounted between bars36, 36a, in any suitable manner. ln this specic embodiment of theinvention, said bars are pro vided with a plurality of regularly spacedgap unit supporting devices which also serve to connect said units inseries electrically. Secured to the bar 36 in spaced arrangement areangular metal bracket plates 39, each having an inwardly extendingcontact piece 40, beveled on its upper edge to facilitate insertion ofthe gap units into the holder, as will appear later. The distancebetween centers of adjacent contact pieces 40, is slightly greater thanthe over-all length of one of the spark gap units already described.Fach contact piece is shouldered or reduced in size at the point 41 toform a smooth joint with a pair of Contact springs 42 secured to theopposite sides of the Contact piece, said contact springs, in their mostdesirable form, extending downwardly and inwardly at a slight angle, asshown. Each of these contact springs has a double bend at its lower endas indicated at 43, constituting a supporting ledger or shoulder for agap unit, and also constituting one member of an automatic circuitcloser when such unit is removed. The springs secured to the adjacentfaces of adjacent Contact pieces 40 press against each other flrml ingood metallic contact as shown at 44 Fig. 3), when not supporting a gapunit, and thus cooperate to provide a separable stirrup or supportingdevice for the reception of such unit. These springs may be of anysuitable form, but as here shown each consists of a narrow strip ofconducting metal having a cut-out portion at 45 of such form thatseparating pressure on a pair of contacting springs results in a uniformbending of both springs back into substantially vertical position,instead of merely a bending of the lower portion of each spring. rlheadvantage of this arrangement, which is very desirable though notindispensable, will appear hereinafter. At each end of the bar 36 arethe half-plate 46, and the half-contact piece 47, corresponding to plate39, and contact 40, respectively; and these end contacts 47, oic whichonly one is shown in the drawing (Fig. 3), each carry only one contactspring 42.

The opposite bar 36, of the frame, also l carries a series of plates andcontact pieces 39L and 40a, corresponding generally to parts 39 and 40before described, and arranged respectively opposite said parts in thesame manner. rllie contact pieces 40ab are however provided withupwardly beveled extensions 48, which project forwardly over and beyondthe bar 36a at the `front of the spark gap device. Half-plates 46a andcontact pieces 47a at opposite ends of bar 36a, correspond to parts 46and 47 on bar 36. The contact pieces on bar 36a are also provided withcontact springs 42a which are similar in all respects to contact springs42 before described, and which also extend downwardly and a shortdistance inwardly toward the center line of the apparatus.

From the foregoing description, it will be seen that if one of the gapunits shown in Figs. 4, 5 and 6 be inserted between two opposite pairsof adjacent contact members 40 and 40a, with the overlapped edges 33 ofthe gap unit vertical, and then gently pushed downwardly, thecorresponding pairs of ad' jacent contact springs 42 and 42a will besprung apart from the position shown at 44 in Fig. 3 and will beseparated, each iinally assuming a substantially vertical position andholding between them the double flanges or tins of the spark gap unit,the outer lower edge of each double lin resting on the stirrup orsupporting portion of a contact spring, while the vertical portion ofthe spring is pressed rmly and lies dat against the oppositeoutersurfaces of the gap unit .anges, making good electrical contacttherewith. Rapid insertion of the gap units is much facilitated by the'upward double bevel on contact pieces 40 and 40a, which serves to guidethe gap unit flanges into proper position. When all of the fifteen gapunits are thus inserted in `the spaces provided for them in the sparkgap holder, it is apparent that said spark gaps are electricallyconnected in series. That is to say, starting with binding postl 49,which is electrically connected to contact'piece 47, current may passthrough the rst contact spring 42 to the copper flange 31 of the gapunit shown at the extreme left in Figs. 2 and 3. The current then passesthrough disks 20, sparking ring 22, jumps the minute gap to thecoperating spark ring 22, passes thence through disk 21 and its attachedlange 31 to the second contact spring 42 of the ser1es, and from theregoes to the iirst complete contact piece 40. The passage ofthe currentthrough the succeeding gap units of the series is the same as alreadydescribedfor the first unit, it being remembered that the contact pieces40a and spring clips 42a on the bar 36a act similarly to 40 and 42 1nconducting current through the ser1es. Incidentally current passes tosome extent d1- rectly from one unit to the next through ianges 200,210, where these happen to abut, as they may in some cases. Binding post50 (Fig. 2) at the opposite end of the serles of 'gap elements iselectrically connected to the half contact piece 47 at that end of theapparatus, so that if the apparatus is connected in the primaryoscillating circuit by means of binding posts 49 and 50, which arearranged at opposite-ends of the holder and are electrically connectedrespectively to the half-contacts 47, and if none of the gap elements iscut out of the circuit or short-circuited, the spark gap apparatus willfunction in the system in the manner characterizing a quenched spark gapcomprising fifteen elementary gaps.

It is especially important to notice that if for any reason it isdesirable to remove anyone of the gap units, or several units, forrepair or for any other purpose, it is only necessary to lift out theunit or units in question, whereupon the spring contact and supportingclips 42 and 42a holding the removed unit or units spring together asindicated at 44 in Fig. 3 thus automatically closing the break in thecircuit at that point.

Another desirable and very important feature of the apparatus is theprovision whereby the number of gaps in circuit may be readily changd soas to enable employment of the gap i connection with transmittingsystems of different power. Thus, a two kilowatt spark gap device,constructed in accordance with my invention, may have its gaps incircuit not only by comparatively large jumps or groups, but also insmall steps whereby fine adjustment may be had at whatever power the gapis set to operate. Means adapted to accomplish both these objects willnow be described.

As has been stated above, in the absence of .any short-circuiting of oneor more gap units, current will pass through the entire series betweenthe binding posts 49 and 50. In order, however, to rovide for rapidlychanging the number o gaps effectively in c1rcu1t,so that the apparatuscan be operated at two or more predetermined different powers, I providea short-circuiting switch device comprising in this instance threeconductive radial switch arms 51, 52 and 53, which are mounted atdifferent angles on a metal switch rod or shaft 54 which extendsparallel to the bars 36 and 36a and is journaled at the front of theapparatus in forwardly projecting extensions of the end members 35 ofthe apparatus frame, as shown. The switch arms are mounted to turn withthe switch rod, and to this end the rod may conveniently be square incross section; but the switch arms are adjustable therealong intodifferent positions opposite any one of the projecting contacts 48,suitable detent means (not shown) being employed to releasablv hold eachswitch arm in any adjusted position lengthwise of the switch rod. Eachswitch arm terminates in a double spring brush as shown, adapted toengage the forward projections 0r blades 48 of contact pieces 40a. Byrotation of the switch rod, any one of the switch brushes can be made toengage the contact 48 opposite which it has been set. The switch rod 54is electrically connected t0 binding post 50 in any convenient' manner,as for example, by way of conductor 55, which leads to half-contact 47aat the right, thence through the cooling iiange of the end gap unit tothe half-contact (not shown) to which binding post 50 is connected, andif the switch rod be turned by means of its operating handle 56 to bringany one of the switch brushes thereon into engagement with the contact48 opposite which that particular switch arm has been set, all the gapunits to the right of that switch arm will be short circuited, and thenumber of gaps actually in service in the system will thereby bereduced. It frequently happens, however, that in operating at any givenpower, finer adjustment is required to obtain a note of the properclearness than would be obaaeeeee tainable by means of the powerchanging device 'with its several switch arms set a considerabledistance apart. Accordingly l provide an auxiliary short-circuitingdevice which may be termed a note clearer, this device being of ysuchcharacter as to enable an increase or reduction of the number of gapelements in series by one gap element at a time, without regard to theparticular setting of the power changer switch. In the form of apparatusshown in Figs. l, 2 and 3, this auxiliary device or note clearerconsists of four switch arms 57 58, 59 and 60 fixed at did'erent angleson a conducting switch rod 61, which extends lengthwise of the apparatusparallel to switch rod 54, and is similarly 'journaled in end members 35of the apparatus frame. That part of switch rod 61 not occupied by theswitch arms may be incased in an insulating sleeve 461"". llifhe saidswitch arms are positioned respectively opposite the four spark gapunits at the left end of the apparatus as shown in Figs. 2 and 3, sothat by turning the switch rod 61 with the aid of operating handle 62,the terminal brushes on 'four switch arms of the note clearer may bemade to engage successively contact pieces 57 a, 58a 59a and 60a, whichare mounted on the front vertical iiace of bar 36a, and each of which iselectrically connected to one of the contact pieces t8. yThe switch rod.of the note clearer is electrically connected as by conductor 62, andscrews 63 and 6ft, to contact piece 47a on bar 36a. rlhis contact pieceis in turn electrically connected by way o' the ange of the last gapunit in series to binding post 49. Consequently, with switch arm 57 or'the note clearer 1n engagement with contact 57a, the iirst gap unit atthe left will be short circuited; and assuming that switch arm 51 of thepower changer is in the posi tion shown in Fig. 3, there will evidentlybe only ve gapsactually in use. lll switch arm 58 be now brought intoengagement with contact 58a, another gap is short circuited. Similarly,three and four gaps can be short circuited by means of switch arms 59and 60, respectively. Lugs 56a adjacent handle 56, coperating with astationary7 stop pin 56h, limit the turning movement of the powerchanger switch rod, and similar means (not shown) may be provided forthe note clearer. lt will b\ noted that the double spring contactbrushes in which the note clearer switch arms terminate are considerablyelongated in the direction ot swing. This is a desirable featurebecause,

' in operating the note clearer, no brush leaves its coperating contactunitl the next succeeding brush has engaged its contact. rllhispractically eliminates sparking.

It is desirable to employ both the power changer switch device and thenote clearer in the apparatus, not only because the note tion with acertain number of gap units ir. l

series, if one of the units should give trouble, it can be immediatelyremoved by the operator in the manner hereinbefore de` scribed,. and thenote clearer can then be shifted to add one more unit to the series.

he circuit having been automatically closed when the defective unit wasremoved, in the manner already pointed out, the apparatus is thusrestored to its original condltion, the necessary operations to eectthis having required but a moment. llt is evident therefore that theapparatus described possesses flexibility of operation to a maximumdegree and can be operated in practice with the minimum amount of delayand trouble. Such considerations are of the utmost im ortance inpractical radio work.

lt is o vious that many changes can be made in the mechanical details otthe holder apparatus above described while realizing the benets of theinvention wholly or in part. F or example, the spark gap units can bemounted on a holder of the type shown in Figs. 7 and 8, and undercertain conditions this typeot holder has distinct advantages on accountof certain `simplified teatures of construction and additional desirablecharacteristics. rThis modied type-of mounting has at least one featurein common with that previously described, that is, an arrangementwhereby removal of any one of the spark gap elements is necessarily accompanied by the closing of the circuit at the point where the spark gapelement was removed, the operation of removing the gap element in thisinstance requiring movement ot a retaining device into such position asto establish the circuit. lin the construction shown in Figs. 7 and 8,the spark gap units are supported between the upper and lower insulatingbars 65 and 66, between which the gap units are inserted and removedlaterally, as compared to the vertical insertion and removalcharacterizing the form of mounting rst described. Mounted on the sideof the upper bar are metal plates 67,

with downwardly depending lugs 68, to each of which lugs is pivoted at69 a combined latch and switch device 70, consisting of two resilientstrips or blades 71 and 72 of metal secured together and electricallyconnected as at 73 by any suitable means. At the rear, member 71 is bentto provide a keeper 74, this keeper also sloping rearwardly from theupper edge of member 71 as clearly shown in Figs. 8 and 10, for apurpose which will presently appear. At the front, member 71 is providedwith a bent portion adording a lifting lug 75 and a retaining lug orkeeper 76. The member 7 2'normally presses at 77 against member 71, butwhen the torward end of the combined retaining and switch member islifted by means of lug 75 into the dotted line position shown in Fig. 8,

` the, forward portion of the combined device operates as a knife switchto engage contact 78 which is supported bg) means of bent brackets 79 tothe plate 67 efore mentioned. On the lower supporting bar 66 are mountedmetal supporting shoes or members 80, each said member belng directlybelow the corresponding latch and switch device 70. These supportingmembers 80 are beveled forwardly as indicated at 81, so that a gap unitmay be readily thrust between a pair of said members, the arrangementbeing such that both double flanges of the gap unit are supported by thebroadened bases of two adjacent members. The method of inserting andremoving gap units from the complete series in this type of mounting isobvious. The latch and switch device 70 being in the position indicatedin dotted lines in Fig. 8, the unit may be readily inserted horizontallyfrom the front, after which the device 70 is turned down into theposition shown in full lines, with blades 71 and 72 pressing against theupper edges of flanges 31 of an adJacent pair of gap units, whilekeepers 74 and 76 substantially engage the rear and front edges,respectively, of the flange of one of the units and prevent displacementthereof. Any desired number of gap units can thus be supported by theholder and electrically connected in series. If now it be desired toremove a gap unit, the member 70 is lifted into dotted line position bymeans of lug 75, whereupon the rearwardly sloping keeper v 74 swingsdown to positively engage the rear Vso edge of the aforesaid flange,slightly tipping the unit forward just after the retaining portion 76 atthe front has been swung out of the way. The unit can then -be withdrawnreadily. It will be seen also that since the member is in electricalcontact with the plate 67 to which it is pivoted, and since when saidmember is swung upwardly it makes electrical contact through 78 and 79to the next succeeding plate 37 'in series, the circuit which wouldotherwise be entirely open by the removal of onev gap unit isnecessarily closed by the act ofremoving such unit. The two plates 67 atthe opposite ends of the series are olf course electrically connected incircuit with the other parts of the transmitter system by suitablemeans. Power changer and note clearer devices of the character beforedescribed may be applied to spark gap apparatus employing this modifiedtype of mounting, a power changer switch rod being indicated at 82 andone of.

its switch arms at 83, the construction in this respect being similar tothat already set forth.

So far as concerns fundamental principles of construction and operation,the spark gap similar in all respects.

apparatus illustrated in Figs. 12 and 13 is practically' the same asthat illustrated in igs. l, 2 and 3. It embodies certain differences instructural detail, however, which afford some practical advantages. Itwill be noted in particular that in the apparatus of Fi s. 12 and 13,the power changer and note c earer devices are arranged atthe rear ofthe series of spark gap units instead of being placed at the front as inthe apparatus of Figsfl, 2 and 3. This makes it possible to materially`shorten the leads connecting the spark gap in circuit with the otherparts of the transmitter, that is, the connections to the condenser onthe one hand and to the primary of the oscillation transformer on theother. This reduces the self inductance of the primary oscillationcircuit and permits operation at lower wave lengths than would otherwisebe possible. As shown, the conducting power changer shaft 100 isrotatably mounted at its ends in the holder frame at a point between thepanel 38 and the spark gap, and carries switch devices 101 arranged atdifferent angles on the shaft which is conveniently squared as before,the switch arms being adjustable longitudinally of the shaft in themanner already described. The switch rod may be turned by means ofoperating handles 102, of which one may be provided at each end. At aconvenient locality, practically at the middle in this instance, theshaft 100 is round in cross section and at this locality an adjustabledouble spring brush 103 embraces the shaft, bearing upon it withsufficient pressure to insure good electrical contact while permittingrelative rotation of the shaft with respect to the brush. To the otherextremity of brush 103 is secured another .brush or spring clip 10-1,the brush being manually operable to move t-he clip 104 into or .out ofengagement with the blade contact 105 which is electrically connected toprimary switch arm 106 of the transmitter wave changer. This switch armcan be swung by means of operating shaft 107 and hand wheel 108, over aseries of Studs 109 which are respectively connected to points on theprimary helix of thel oscillation transformer.

The note clearer device comprises in'this embodiment of the invention arod 110 of insulating material rotatably journaled at its ends in theholder frame and carrying a metal sleeve 111, to which are secured thenote clearer switch devices 112, five in number in this instance. Theseare arranged at vdifferent angles in the same manner as thecorresponding switch devices of the note clearer shown in Figs. 1 to 3,and their function and mode of operation are' essentially The noteclearer switch rod can be turned by means of operating 'knob 1108. Anad'ustable double spring contact brush 113 ears upon the sleeve 111 andis electrically connected at 114 to condenser 37.

The path of the current between the condenser and the primary helix P ofthe transmitter can, therefore, be traced as follows: Starting with thecondenser, current flows through brush 113 to sleeve 111, thence throughone of the note clearer switch d evices 112 to the contact 57a withwhich said switch device is engaged, thence through the series of gapunits being used to whichever one of the contacts 4:8 is engaged by oneof the switch devices 101; and from there through shaft 100 and 1brushes103 and 104, [blade 105 and switch arm 106 to a point on the transformerprimary represented by one of the studs 109.

This arrangement not only permits the use of shorter wave lengths andthereby 1ncreases the `effective range of operation, but it also has thefurther advantage that such spark gap units as are not actually beingused are entirely cut out of circuit; whereas in the apparatus shown inFigs. 1, 2 and 3, the spark gap units not in service are 1n a sensesimply shunted by the short circuiting action of the power changer andnote clearer.

1t is found that the arrangement of Figs. 12 and 13 results in somewhatmore perfect performance of the spark gap, although the yarrangementfirst described is entirely. satisfactory for all practical purposes.

As a matter of convenience it is desirable that in operating the powerchanger switch and the note clearer switch, the operator may be able tovtell by the sense of touch the points at which the several switchdevices 101 and 112 are in operative position. To this end, theparticular apparatus sho-wn in Figs. 12 and 13 is provided with detentmeans comprising, in the case of the power changer switch, a leaf spring113a having a forked upper end provided with sharp angular bends 114awhich are adapted to enter coperating notches formed on the face of acollar 115a, secured to the shaft 100. The turning movement of shaft 100may Ibe limited by means of a stop 56d formed on the leaf spring 1131,said stop lying in the path of lugs 56" formed on the collar 1153.Releasable detent mechanism similar to that described for the powerchanger switch may also be provided for the note clearer, as indicatedat lieb, 1141 and 115D. A limiting Stop device (not shown) may also beemployed with the' note clearer switch.

r1`he apparatus illustrated in' Figs. 12 and 13 while suitable for sparkgap apparatus of any desired power is typical of a 1 kilowatt spark gapwhich has given satisfaction in actual use. As here shown, the spark gapunits 116 may be of the type illustrated in Fig. 6, with the verticaldimension of the rectangular cooling flanges less than the horizontaldimension. The arrangement'for 'hold said geg supporting the gap unitsand electrically connecting them 1n series is substantially ashereinbefore described in connection with Figs. 1, 2 and 3.

As before stated, the present invention enables the construction of selfcooled quenched gaps which are much lighter and less bulky than gaps ofthe power heretofore constructed. 1n a specific instance, 'a 2 kilowattspark gap constructed in accordance with the present disclosure weighedabout pounds, whereas heretofore the minimum weight for a 2 kilowattself cooled quenched gap Moreover the gap constructed in accordance withmy invention, occupied very much less space and heated up to only aboutdegrees C., whereas the old type of gap operating under exactly parallelconditions heated up to about 120 degrees C. 1t will be evident also, inaddition 'to the other advantages of the invention hereinbefore pointedout, that by providing separate self-contained gap units, whosecomponent electrode members are assembled and secured together inaccurate spaced relation by individual clamping means the elementary gapdistances are not disturbed in any way when the gap units are assembledin series as herein set forth; whereas in the former practice, all theelectrode plates or disks of the complete gap were clamped together bypressure means acting on the series as a whole, anarrangement whichinvariably operated to disturb the elementary gap distances.

Although certain specific embodiments of the broad invention areillustrated in the drawings and have been set forth in detail in theforegoing description for purposes of explanation, it is to beunderstood 'that the invention contemplates a wide range of variationsin mechanical details of construction and arrangement, and comprises allsuch variations as fairly come within the scope of the appended claims.

`What 1 claim is: 1. A spark gap device comprising a pair of electrodemembers insulated from one another an having coperating annular sparkingsurfaces disposed in parallel closely spaced relation, in combinationwith means extending between said members centrally of said sparkingsurfaces and serving to members firmly together in operative relation,said device constituting a removable gap unit adapted for use in serieswith similar gap units ina complete spark gap.

2. A spark gap device comprising a plurality of electrode membersinsulated'from one another and having coperating annular sparkingsurfaces disposed in substantially parallel closely spaced relation, incombination with transversely disposed fastening means extending withinthe inner peripheries same operating was 150 pounds.

of said sparking surfaces and serving to clamp said members together in.operative relation, said device constituting a removable gap unitadapted for use in series with similar gap units in a complete sparkgap.

3. A spark gap device comprising a pair of electrode members insulatedfrom one another and having coperating circular annular sparkingsurfaces disposed in parallel closely spaced relation, in combinationwith a bolt extending within the inner peripheries of said sparkingsurfaces, said bolt threading into one of said members and extendingthrough the other said member, said bolt being insulated from such othermember but arranged to` clamp the same in operative relation to thefirst member.

4:. A spark gap device comprising a pair of electrode members insulatedfrom each other, a clamping bolt threading into one of said members andextending through an opening in the other member but out of contacttherewith and having a suitable head, and a bearing washer insulatedfrom such other member, but arranged to transmit clamping pressurethereto from the bolthead.

5. A spark gap device comprising electrode members insulated from eachother, said members having cooperating sparking surfaces on theiradjacent faces, and having their opposite non-adjacent faces recessed,in combination with means holding said members together and disposedwholly between the outer planes of said non-adj acent faces.

6. A spark gap device comprising a pair of plate electrodes havingcoperating sparking surfaces, a headed bolt extending through oneelectrode but insulated therefrom and anchored to the other electrode,and a washer disposed between the bolt head and the iirst electrode butinsulated from the latter, the coperating surfaces of said washer andbolt head being formed to localize the pressure between them.

7. A spark gap device comprising a pair of plate electrodes suitablysecured together in operative relation as a unit, and a double coolingflange of sheet metal on each member, each double flange having itsedges connected at two opposite localities and free at two otheropposite localities;

8. A spark gap device comprising a. pair of plate electrodes suitablysecured together in operative relation as a unit, and a doublerectangular cooling flange on each member, said flange having one pairof opposite edges substantially continuously connected, and the gtherpair of opposite edges substantially ree.

9. A spark gap device comprising coperating sparking electrodes, incombination lwith cooling means in heat conducting relation to saidelectrodes and consisting of conducting material formed to provide aflue for circulation of cooling air.

l0. A gap device comprising cooperating spark gap electrodes, incombination with metal cooling fins or flanges of such thinness that thetemperature gradient in said ns is relatively high, said fins beingformed to provide iues for passage of cooling air upwardly.

11. A spark gap device comprising plate electrodes having coperatingsparking surfaces on their adjacent faces, said adjacent faces beingalso provided with coperating bearing flanges or ribs surrounding saidsparking surfaces and having narrow rounded bearing surfaces, aninsulating gasket interposed between said coperating bearing flanges orribs, and means clamping said members together.

12. Quenched spark gap apparatus comprising a plurality of sparkelectrodes cooperating to provide serially related elementary gaps incombination with switch means operable to vary, by relatively largesteps, the number of such gaps effectively in circuit, and additionalswitch means operable to vary, by relatively small steps, the number oflsuch gaps effectively in circuit.

13. Quenched spark gap apparatus comprising a holder, a plurality ofspark electrodes arranged ina plurality of structurally separate groupsindividually removable from said holder, said electrodes coperating toprovide serially related gaps, in combination with switch devicesoperable to vary the number of such gaps effectively in circuit byrelatively large steps and by relatively small steps, respectively.

14. Quenched spark gap apparatus comprising a plurality of spark gapunits electrically connected in series, in combination with switch meansadapted for connection in an oscillation circuit and operable to makeconnection with different gap units near one end of the series, andladditional switch means also adapted for connection in an oscillationcircuit and operable to make connection with different gap units in theremainder of the series.

15. Quenched spark gap apparatus comprising a plurality of spark gapunits electrically connected in series, in combination with switch meansadapted for connection in an oscillation circuit and operable to makeconnection consecutively with a certain number of gap units beginning atone end of the series, and additional switch means also adapted forconnection in an oscillation circuit and operable to make connection inregular sequence with different gap units in the remainder of theseries.

16. Quenched spark gap apparatus comprising a plurality of sparkelectrodes cooperating to provide serially related eleaeeaeec mentarygaps, in combination with switch means operable to vary the number ofsuch gaps efe'ctively in circuit by definite steps, said switch meansbeing adjustable to alter the extent of said steps.

17. Quenched spark gap apparatus comprising a plurality of Sparkelectrodes cooperating to provide serially related elementary gaps, incombination with switch means adapted for connection in an oscillationcircuit and having a plurality of switch arms movable to make electricalconnection selectively with different spark electrodes and thereby tovary the number of gaps effectively in circuit.

18. Quenched spark gap apparatus comprising a holder, a plurality ofspark gap units of the plate type mounted on said holder andelectrically connected in series, contact devices each electricallyconnected to a point in the gap series, and switch means adapted forconnection in an oscillation circuit and movable to engage said contactdevices selectively in predetermina-ble sequence andthereby to vary theeiiective number of gap units in circuit.

19. Quenched spark gap apparatus comprising a holder, a plurality ofspark gap units mounted thereon and electrically con` nected in series.a plurality of contact devices electrically connected to differentpoints in the series or gap units, an elongated switch member having aplurality of switch arms spaced apart along said member and extendingradially therefrom at dii'- ferent angles, said switch member beingrotatable to bring said switch arms successively into engagement withcertain of said contact devices.

20. Quenched spark gap apparatus comprising a holder,'a plurality ofspark gap units mounted thereon and electricallyconnected in series, aplurality of contact deJ vices electrically connected to oliiierentpoints in the series of gap units, an elongated switch member having aplurality of switch arms spaced apart along said member and extendingradially therefrom at ditferent angles, said switch member beingrotatable to bring said switch arms successively into engagement withcertain of said contact devices, said switch arms having contactportions so arranged that none of the switch arms breaks contact withits corre! sponding contact device until another switch arm has begun toengage its corresponding contact device.

2l. Quenched spark gap apparatus comprising a plurality of coperatinggap units, in combination with switch means operable to make electricalconnection in sequence with different gap units of said plurality forthe purpose of including di'erent numbers of said units in anoscillation circuit,

the arrangement being such that connection to one unit is not brokenuntil connection to another has been made.

22. Quenched sparkgap apparatus comprising the combination, with aholder, of a plurality of individually removable spark gap unitselectrically connected in circuit, the arrangement including meansoperable by removal of a gap unit to prevent a break in the circuit bysuch removal.

23. Quenched spark gap apparatus comprising the combination, with aholder' provided with conductive supporting devices, of a plurality ofspark gap units supported and connected in circuit by said devices, thearrangement being such that removal of a gap unit closes the circuit atthat point.

24:. Quenched spark gap apparatus comprising the combination, with aholder having supporting devices coperating in pairs to supportindividually removable spark gap units and to connect said units incircuit, said devices being also operable to prevent -a break in thecircuit when a unit is removed.

25. Quenched spark gap apparatus comprising, in combination, parallelsupporting members, spark gap units individually insertible between saidsupporting members, and means arranged to receive and hold said gapunits in position between said supporting members, said means alsoserving to electrically connect said gap units in series whilepermitting them to be individually withdrawn from the series.

26. Quenched spark gap apparatus comprising, in combination,substantially horizontal parallel bars provided with a plurality or"opposed pairs of depending supporting devices, and coperating spark gapunits having cooling flanges arranged to engage said supporting devices.27. Quenched spark gap apparatus comprising holder means provided with aplurality of insulated conductive supporting devices, and coperatingspark gap units having cooling flanges arranged to engage saidsupporting devices.

28. Quenched spark gap apparatus comprising, in combination,substantially horizontal parallel bars provided with a plurality ofopposed pairs of depending conductive supporting devices, and spark gapunits having cooling flanges arranged to engage said supporting devices,said devices being arranged to connect the gap units in series.

29. Quenched spark gap apparatus comprising, in combination,substantially horizontal parallel bars provided with a pluralityy ofopposed pairs of depending contact springs, and spark gap units arrangedto engage said Contact springs and to be connected thereby in series,`said contact springs being arranged to automatically close a break inthe circuit occas1oned by removal of a gap unit.

' ent contact members which tend Vto remain in contact but which areseparable by insertion of a spark gap unit therebetween, each suchdevice on one bar being adapted and arranged to coperate with another ofsa1d devices on the other bar to support a spark gap unit and toelectrically connect it wlth adjacent units.

32. A spark gap holder comprising a pair of insulating bars spaced apartand substantially parallel, a plurality of gap unit holding memberscarried by said bars and adapted to engage and connect in series sparkgap units, contact devices electrically connected, respectively, tocertain of said holding members, and a rotatable switch devicecooperating with said contact devices and adapted forconnection in anoscillation circuit.

33. A spark gap holder comprising, in combination, an insulatingmounting frame or base including substantially parallel spacedinsulating bars, a plurality of gap unit holding members carried by saidbars and adapted to engage and connect in series spark gap units, aseries of contact devices connected to certain of said holding membersand arranged adjacent one of said bars and substantially parallelthereto, a switch device including a conductive switch rod rotatablymounted on said frame substantially parallel to said bars and adjacentsaid contact devices and having radial contact arms mounted at differentangles on said switch rod and arranged to engage certain of said contactdevices in regular sequence when the switch rod is rotated.

34. A spark gap holder comprisin in combination, an insulating mountingrame or base includin substantially parallel spaced insulating bars, aplurality of gap unit holding members carrled by said bars and adaptedto engage and connect i'n series spark gap units, a series of contactdevices connected to certain of said holding members and arrangedadjacent one of said bars and substantially parallel thereto, a switchrotatably mountedon said .frame substantially parallel to said bars andadjacent said contact devlces and having radial contact arms mounted atdifferent angles on said switch rod and arranged to engage certain ofsaid contact devices in regular sequence when the switch rod is rotated,a second switch device operable to engage certain others of said contactdevices, and means adapting both switch devices for connection in anoscillation circuit.

35. A spark gap holder comprising an insulating supporting structure,means on said supporting structure for mounting thereon a plurality ofspark electrodes electrically connected in series, in combination withtwo separate switch devices mounted on said structure and operable toinclude in circuit between them a variable number of such electrodes,and means for directly connecting both switch devices in an oscillationcircuit.

36. Quenched spark gap apparatus comprising, in combination, a pluralityof structurally separate spark gap units each comprising coperatlngelectrodes provided with multiple cooling flanges consisting of spacedcomponent flange elements suitably connected together, and meansmaintaining said gap umts in operative assembly, the arrangement beingsuch that the adjacent multiple flanges are spaced apart a distancesubstantially equal to the spacing of the component flange elements.

37. Quenched spark apparatus comprising a plurality of coperating sparkgap units, in combination Vwith means for adjusting the circuit relationof said units for operation at different selected powers, and means foradjusting the character of the note produced at each operating power.

38. Quenched spark gap apparatus comprising the combination, with aholder, of a plurahty of cooperating electrode plates or disks supportedthereby, said electrode plates or disks being arranged in electricallyconnected units, each unit having its component plates or disks securedtogether in operative relation independently of the other units, andeach unit being insertible into and removable from the apparatus withoutdisturbing the other units.

39. A spark gap device comprising cooperating spark electrodes, incombination with relatively thin coperating cooling ns spaced apart adistance of between .2 inch and .4 inch as approximate limits, saidcooling fins being constructed of highly conductive sheet metal andbeing arranged to provide upright llue means.

40. In radio transmitter apparatus, the combination wtih oscillationcircuit connecting terminals, of a quenched spark gap, two sw1tchdevices mounted closely adjacent tween them in circuit a said terminalsand operable to include a variable proportion of said spark gap incircuit, and means for connecting said switch devices to said terminals.

41. In radio transmitter apparatus, the combination, in anoscillationcircuit, of a quenched spark gap, two switch devices operable to includebetween the main circuit a variable proportion of said gap, and leadsconnecting said switch devices respectively in said oscillation circuit,the spark gap being otherwise unconnected in the circuit.

42. In radio transmitter apparatus, the combination, with a wave changeswitch, and a condenser, of a quenched spark gap, two `switch devicesadjustable to include bevariablc proportion of said spark gap, and meansfor electrically connecting one of said switch devices to said wavechange switch and the otherV switch device to said condenser.

43. In radio transmitter apparatus, the combination, with a suitablymounted wave change switch, and a condenser and a quenched spark gapmounted substantially therebelow, of two switch devices locatedsubstantially between said spark gap and said condenser andirespectively connected to said wave change switch and to said condenser,said switch devices being adjustable to include between them a variableproportion of said spark gap.

44. Spark gap apparatus, comprising a plurality of independentlyremovable spark gap units connected in series, and means forautomatically closing the circuit between adjacent l{gap units whenA agap unit is removed.

45. unit sparkgap, comprising a plurality of electrode plates assembledtogether iiatwise and provided with annular sparking plates the sparkingfaces of which are spaced apart to provide a spark gap space betweenthem, the electrode plates having bea-ring faces extending about thesparking plates and spaced therefrom and being secured together with aninsulating and airexcluding packing between their bearing faces by asingle central screw bolt extending through an opening in oneof theplates and through the openings in the sparking plates and into a blindtapped hole in the other electrode plate, insulating and air-excludingpacking being provided between the head of the screw bolt and the wallsof the opening in the electrode plate through which the bolt extends.

46. Spark gap apparatus, pluralityof gap unit holders of a pair ofspring conducting arms to bear .against and support a gap unit andthrough which electrical connection is made to the opposite sides of thegap unit, a terminal connected to the outer arm of each end holder andother terminals connected each to the adjacent arms of two adjoiningholders, two contact members for making contact with said .terminals toconnect the holders in the circuit, and means for causing a comprising a`relative movement between said contact members for varying the numberof holders connected in the circuit and for moving said contact memberstogether for connecting any desired series of the holders in thecircuit.

In testimony whereof I hereunto ax my signature.

narra LowENsfrmN. i

each formed g

